The British Balfour Declaration in 1917 stated “His Majesty’s government view with favour the establishment in Palestine of a national home for the Jewish people, and will use their best endeavours to facilitate the achievement of this object, it being clearly understood that nothing shall be done which may prejudice the civil and religious rights of existing non-Jewish communities in Palestine, or the rights and political status enjoyed by Jews in any other country.”
This was followed by the 1922 Palestinian Mandate by the League of Nations. But after WWII the Jewish population demanded independence from the British, and fought for it. The UN approved the creation of the State of Israel, but in the meantime fighting between Jews and Arabs escalated.
In May of 1948, the British left, and the Jewish agency, led by David Ben Gurion, declared the creation of the State of Israel. In May of 1949, an armistice was reached with a defined border.
Efforts to partition the land for Palestinians and Jews met resistance from both sides.